1. Field of the Invention
The present invention relates to a vehicle body front structure having closed-section torque boxes for joining frames and side structures.
2. Description of the Related Art
In general, in a front structure of a vehicle such as an automobile, front frames extend in a longitudinal direction of a vehicle body along inner sides of wheel aprons constituting side walls of an engine compartment. The front frame inclines downwardly to connect to a floor frame from a toe board, as a boundary, which separates a passenger compartment from the engine compartment. On the other hand, a side structure which defines the vehicle width is disposed outwardly of the frame by the width of a wheel well in which a wheel is accommodated. The side structure is constituted by a front pillar and a side sill which is connected to a lower end portion of the front pillar to form a step portion or the like. A toe board portion constitutes a rear portion of the wheel well and joins the frame and the side structure in a transverse direction.
However, the rigidity of a portion in the vicinity of the rear end portion of the front frame cannot be sufficient with the construction in which the front frame is joined to the side structure only by the toe board. In case an excessive impact load is applied to the front frame from the front, not only the deformation behavior at the rear end portion of the front frame become uncertain but also the dispersion of the impact load to the side structures becomes insufficient, there being caused a risk that the front frame starts to deform too early. To cope with this, a torque box is disposed between the front frame and the side structure in order to assist the toe board in allowing the side structure to effectively bear the load applied to the front frame.
Conventionally, a torque box structure disclosed in JP-A-7-165118 which is in FIG. 8 as a first conventional example and a dash panel structure disclosed in JP-A-2000-16333 which is shown in FIG. 9 as a second conventional example are taken as a torque box disposed to complement and reinforce the toe board which joins the front frame to the side structures as described above. The first conventional example shown in FIG. 8 is constructed such that a flange for joining a rear portion 22 of a front side member (a front frame) 21 to a dash panel (a toe board) 26 is extended downwardly so as to overlap a floor member of a torque box 27 for joining a side structure including a front pillar 24 and a side sill 25 to the front side member 21, so that the rigidity of the flange is increased, whereby the weight of the dash panel is reduced and the welding performance is also improved. Reference numeral 35 denotes a wheel well.
On the other hand, the second conventional example shown in FIG. 9 is constructed such that a dash panel 46 is divided into half so as to form a closed-sectional structure at the divided portion with upper and lower panels, that a rear end portion 42 of a front side member 41 is connected to the closed-sectional structure, and that the closed-sectional structure is extended as far as a proximal portion of a front pillar 44 to be joined thereto. Then, a torque box 47 for joining a frame to a side structure including the front pillar 44 and a side sill 45 is disposed at a lower portion of the dash panel 46 or a portion of the rear end portion 42 of the front side member 41 which inclines downwardly to connect to a floor frame 43, whereby the impact load from the front is borne by the closed-sectional structure to transmit part of the impact energy to the front pillar 44 or the like without providing any particular cross member but with a light and inexpensive structure. Reference numeral 55 denotes a wheel well.
In the vehicle body front structure incorporating the conventional torque boxes, however, any of the torque boxes for joining the front side member to the side structure is joined to the inclined portion where the rear end portion of the front side member is joined to the floor frame one step down or to a portion of the floor frame rearward of the inclined portion. Then, in case an excessive impact load resulting from a frontal collision is applied to the front side members, there has been caused a risk that the front side members start to deform toward the interior of the passenger compartment before the sufficient transmission or dispersion of the impact load through the torque box is attained. Moreover, with the second conventional example, the closed-sectional structure is formed at the divided portion of the dash panel using the upper and lower panels, and this calls for an increase in production costs since separate fabricating processes are involved, and additionally a complicated structure cannot be avoided.
Then, an object of the present invention is to provide a vehicle body front structure which can solve the problems inherent in the vehicle body front structures incorporating therein the conventional torque boxes, improve the rigidity at the rear end portion of the front frame and attain the sufficient transmission or dispersion of impact load to the side structures only with a simple structure.
To attain the object, according to a first aspect of the present invention, there is provided a vehicle body front structure including: a frame having a front frame and a floor frame joined together by a curved portion provided along a toe board, the front frame extending in a forward direction from the curved portion, the floor frame extending in a rearward direction therefrom; a side structure disposed transversely outwardly of the frame, respectively; and a closed-section torque box for joining the frame to the side structure, wherein the frame and the side structure are joined to an upper surface of the torque box to be substantially horizontally relative to each other, and the frame and the side structure are joined to a lower surface of the torque box which is formed in such a manner as to be oriented downwardly toward the side structure, to thereby increase the joint area of the torque box on a side thereof where the torque box is joined to the side structure.
Further, according to a second aspect of the present invention, there is provided a vehicle body front structure including: a frame having a front frame and a floor frame joined together by a curved portion providing along a toe board, the front frame extending in a forward direction from the curved portion, the floor frame extending in a rearward direction therefrom; a side structure disposed transversely outwardly of the frame, respectively; and a closed-section torque box for joining the frame to the side structure, wherein the torque box is joined to the frame in such a manner as to extend from the front frame to the curved portion.
According to a third aspect of the present invention, there is provided a vehicle body front structure according to the first or second aspect of the present invention, wherein the curved portion is joined to a lower surface at a rear end of the front frame.
According to a fourth aspect of the present invention, there is provided a vehicle body front structure according to any of the first to third aspects of the present invention, wherein the torque box is formed into a shape of a closed-section by a gusset disposed on an engine compartment side and the toe board joined to the gusset and disposed on a passenger compartment side, and wherein a first joint surface and a second joint surface are formed on an upper surface and a lower surface of the gusset, respectively, in such a manner as to be joined to corresponding surfaces of the toe board.
According to a fifth aspect of the present invention, there is provided a vehicle body front structure according to the fourth aspect of the present invention, wherein a third joint surface is formed from a front surface of the gusset toward the toe board.
According to a sixth aspect of the present invention, there is provided a vehicle body front structure according to any of the first to fifth aspects of the present invention, wherein the torque box is divided into a first torque box disposed transversely inside and a second torque box disposed contiguously with the first torque box and transversely outside.
According to a seventh aspect of the present invention, there is provided a vehicle body front structure according to the sixth aspect of the present invention, wherein the toe board is disposed on a passenger compartment side of the first torque box, between the first torque box and the second torque box and on an engine compartment side of the second torque box.
Thus, the rigidity of the portions in the vicinity of the rear end portions of the front frames is ensured by disposing the uniquely configured torque boxes between the front frames and the side structures, and the impact load can be transmitted or dispersed sufficiently to the side structures from the initial stage of deformation of the front frames, so that the front frames are allowed to deform in a stable fashion, whereby the damage to the passenger compartment can be minimized.